PCM1808 SCLK

[plasmaphase]

I'm currently using an ESP32-S3 to connect to a PCM1808 Audio ADC (https://www.ti.com/lit/gpn/pcm1808). The standard i2s example seems sufficient with one exception, the SCLK. The PCM1808 part requires a clock input which is it's sample clock:

PCM1808_Pinout.png (138.84 KiB) Viewed 5326 times

SystemClock.png (149.81 KiB) Viewed 5326 times

In the i2s standard example (https://github.com/espressif/esp-idf/bl ... ple_main.c) there's the MCLK, BCLK, WS, and DOUT, but there is no SCLK:

i2s_pins.png (26.81 KiB) Viewed 5326 times

So my question is, is there a way to create a "generic" clock output on a GPIO pin that's synchronous with other pins? Is there another more novel solution to this? The PCM1808 requires this clock to function, and surely there has to be a way to generate this clock, I'm just not familiar enough to know how.

[ESP_Sprite]

Looks like 'system clock'/SCLK is TIs equivalent to MCLK.

[plasmaphase]

You may be right, I will try connecting as MCLK and try it out.

[clearlynotstefan]

You may be right, I will try connecting as MCLK and try it out.

Did it work? I'm looking at picking one of these up for a project and concerned about this issue as well.

[jenschr]

@plasmaphase I'd also love to know if MCLK was the answer

[escalator]

@plasmaphase I'd also love to know if MCLK was the answer

Hi, yes the GPIO0 pin carries out the MCLK signal from I2S by default in the ESP32, it can go directly to pin 6 of PCM1808 (SCKI) or, better, you can do it through a 10 to 49 ohm resistor. As an example for plain ESP32 chip:

Code: Select all

#define SAMPLERATE  48000
#define BITS	16
#define NUMCHANNELS 2
i2s_config_t i2s_config = {
	                .mode = I2S_MODE_MASTER | I2S_MODE_RX,
	                .sample_rate = SAMPLERATE,
	                .bits_per_sample = BITS,
	                .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
	                .communication_format = I2S_COMM_FORMAT_STAND_MSB,
	                .dma_buf_count = 4,
	                .dma_buf_len = 240,
	                .use_apll = true,
			.fixed_mclk = 256 * SAMPLERATE,
			.tx_desc_auto_clear = true,
	                .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1                                //Interrupt level 1
	};

In my example I fix the initial MCLK rate at 256 x sample rate, you can modify it to your needs or change it later in code.

Code: Select all

//I2S pinout example configuration
	i2s_pin_config_t pin_config = {
	                .bck_io_num = 5,//BIT CLOCK(TO PIN 8 BCK IN PCM1808)
	                .ws_io_num = 25,//LR CLOCK(TO PIN 7 LRCK IN PCM1808)
			.mck_io_num = 0,//MASTER CLOCK(TO PIN 6 SCKI IN PCM1808)
	                .data_out_num = -1,//(NOT USED)
	                .data_in_num = 35//DATA IN(FROM PIN 9 DOUT IN PCM1808)
	};
 	ESP_ERROR_CHECK(i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL));
 	//this optional line reconfigures the default I2S asignment pins:
  	ESP_ERROR_CHECK(i2s_set_pin(I2S_NUM_0, &pin_config));
  	//this optional line configures the default MCLK rate:
  	ESP_ERROR_CHECK( i2s_set_clk(I2S_NUM_0, SAMPLERATE, BITS, NUMCHANNELS) );
  	

[jenschr]

Thanks! Got it running as well.

[MariusD]

Hi guys,

I am using your sample code and I can see all of the clocks being sent to the PCM eval board. Unfortunately, it is not sending back any data when it is in slave mode, only when I use the onboard master oscillator.

Are there any other configs or timings missing from the sample code?

[MariusD]

Thanks! Got it running as well.

Are you able to paste the working I2S read calls that decode the data? I am having trouble decoding the data stream.